This invention relates to carburetors and more particularly to a staged-type carburetor whose fuel metering signal is modulated to control the air-fuel ratio of the mixture produced in the carburetor.
Staged-type carburetors are designed to have performance characteristics approximating those of a non-staged type or conventional carburetor having more barrels or induction passages than the staged carburetor. Thus, for example, the operating characteristics of a staged two-barrel carburetor should approximate those of a corresponding non-staged four-barrel carburetor. In one design for a staged two-barrel carburetor, the pressure drop or fuel metering signal created at a venturi in the carburetor's induction passage was experimentally found to be approximately four times that normally created in a non-staged carburetor. Since the flow rate of fuel through a carburetor's fuel circuit is proportional to the pressure drop created in the carburetor's induction passage, much more fuel is delivered to the induction passage than is required for proper engine operation and an air-fuel mixture is produced in the induction passage which is too rich.